Conventionally, attempts have been made to use surplus electric power and the like to rotate a flywheel supported by bearings and store the energy as the energy of the rotary motion of the flywheel. To do so, the rotational resistance of the flywheel is reduced as much as possible, and essentially, it is rotated in a resistance-free state.
In actual fact, a flywheel that is given floating support using the fishing effect (pinning effect) of superconductors that can restrict and hold lines of magnetic force that penetrate internally and reduces the frictional resistance of the bearing part to an extreme degree is used.
An example is disclosed in Japanese Patent No. 2992578, wherein the flywheel described is formed in the shape of a disk or the shape of a ring.
However, conventional disk-shaped or ring-shaped flywheels give rise to the following problems.
In other words, it is theoretically possible to increase the amount of energy stored by producing the flywheel from a material that is comparatively light in weight with high tensile strength, for example, carbon fiber reinforced plastic (CFRP) or the like, and rotating the flywheel at an even higher speed.
CFRPs are carbon fiber reinforced plastic thermosetting resins that use carbon fibers in a manner similar to glass fiber reinforced plastics (GFRP), which have continuous fibers, woven fabric, short fibers and the like for glass fibers hardened by a thermosetting resin, such as unsaturated polyester resin or epoxy resin.
In addition, when the tensile strength of CFRP materials is calculated, it is possible that the speed at the periphery of a flywheel increases to approximately 1800 m/sec.
However, when the periphery of the flywheel reaches a speed of approximately 800 m/sec with disk shaped or ring shaped flywheels, strain and deformation arise in the flywheel itself because of the centrifugal force from the rotation; therefore, the rotational balance of the flywheel breaks down, shaft vibration increases, and the rotational speed cannot be increased above that.
Therefore, it is technically difficult to increase the speed of rotation so that the speed at the periphery of the flywheel is greater than approximately 800 m/sec.